Date: Spring 2012
Why have bacteria evolved resistance so rapidly?
Suppose you have a bug spray and you use it to exterminate a cloud of
In the cloud of mosquitoes there may be one or two that are immune to the
effects of the bug spray.
So what you do is kill all the mosquitoes that don't have resistance to the
Leaving behind the mosquitoes that do, and then those remaining mosquitoes
That is the sad story of how bugs develop resistance to our countermeasures.
So far, we have always been able to find a bug spray formula to take care of
the present cloud of mosquitoes.
To answer your question, a couple of things need to be considered.
First, bacteria replicate using binary fission, which is cell replication.
Bacteria like E. coli have a new generation approximately every 15 minutes.
Other bacteria may take a little longer to replicate for a new generation
but this is a short amount of time.
According to the theory of natural selection, organisms have methods of
adapting to their environment and will pass that onto their offspring.
Since bacteria replicate with binary fission, something else had to happen
during their evolution to get genetic variability so they could adapt.
Bacteria are able to get genetic material from their environment and
incorporate it into their genetic material in 3 ways, depending on the type
One way is called conjugation that involves using a pilus, which is a
hair-like structure to make a connection between a donor and receptor cell.
Another way is called transformation where free DNA in the environment,
which can be from other types of dead bacteria, is incorporated into what is
called a competent cell. The third way is called transduction where a
bacteria virus transfers DNA from one cells to another.
Many antibiotics target the manufacturing of a protective layer called
peptidoglycan that is only found in bacteria. The type of resistance to an
antibiotic will be specific to that antibiotic. A way is found in bacteria
to get-around the process that is being targeted. The more information that
is found in how bacteria work helps in researching new types of antibiotics.
If the short time it takes bacteria to replicate plus their ability to
incorporate outside genetic material into their DNA is combined with an
increase in the use of antibiotics, that would explain an increase in
bacteria that are resistant to antibiotics.
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Update: June 2012